1. Technical Field
The present disclosure relates to methods and apparatus for imaging biological tissue employing both X-ray and ultrasound technology to provide enhanced diagnostic capability. In particular, the present disclosure provides a combined ultrasonic and an X-ray imaging system that provides registered X-ray and ultrasound images.
2. Background of Related Art
The use of X-ray technology for providing two-dimensional images of biological tissue for diagnosis of carcinoma or other tissue abnormalities is well known. However, X-ray imaging has a number of limitations which are universally recognized by radiologists, such as, for example, that X-ray images provide only a two-dimensional image of a three-dimensional object. Thus, although a potential area of concern may be indicated, the precise location of the subject area within the tissue may be uncertain.
In addition to conventional radiography machines, an apparatus has been developed that employs ultrasound technology for imaging biological tissue. Ultrasound imaging devices display echoes received from a transducer as brightness levels proportional to the energy reflected by the tissue components. These brightness levels are displayed at the appropriate echo range and transducer position or orientation, resulting in a cross-sectional image of the object in a plane perpendicular to the transducer emitting face.
Heretofore, the advantages offered by ultrasound technology have long been recognized by the medical community, construction of previously known radiography and sonography equipment has prevented combination of these two technologies.
Specifically, polycarbonates such as Lexan.RTM., are typically used in radiography machines because of their tensile strength and transparency to X-ray radiation. These materials are substantially acoustically opaque, however, and tend to distort most ultrasonic signals traversing these materials, as described in U.S. Pat. No. 5,479,927 which is herein incorporated by reference. On the other hand, the compression plates used in previously known ultrasound devices, for example, as described in U.S. Pat. No. 3,765,403, are composed of materials such as polystyrene or polyurethane, which have insufficient tensile strength for use in radiography equipment.
Several previously known devices, such as described, for example, in WO Publication No. 83/02053, have sought to achieve spatial registration between X-ray and ultrasound images. Such devices, however, have required movement of the tissue between the X-ray and ultrasound imaging steps, thereby preventing accurate correlation of the two images.
In view of the foregoing drawbacks of previously known imaging apparatus and methods, it would be desirable to provide an apparatus and methods for providing registered X-ray and ultrasound images of biological tissue.